This invention relates in general to printed circuit boards, and in particular to a reconfigurable printed circuit board for field programmable devices.
Printed circuit boards (PCBs) facilitate rapid construction of electronic circuits by providing a stable insulating sheet of material upon which circuit components are mounted. The components are typically interconnected using thin plated conductive (e.g. copper) lines bonded to the sheet that form circuit paths. A large variety of PCBs has been developed for many different applications.
Field programmable devices (FPDs) are circuits that include a large number of gates whose interconnection can be programmed to form a desired logic function. Utilizing any one of a variety of reprogrammable technologies, FPDs allow engineers to electrically program (and reprogram) standard, off-the-shelf logic elements to meet the specific needs of their application. Thus, FPDs combine the logistical advantages of standard, fixed integrated circuits with the architectural flexibility of custom devices. For the purposes of this description, it is to be understood that a programmable device refers to once programmable as well as reprogrammable devices.
Larger and more complex circuits can be developed by combining and interconnecting several FPDs on a PCB. A growing field of application for such boards is design and rapid implementation of prototypes for larger systems such as a microprocessor. Using computer aided design (CAD) tools and versatile FPD-based PCBs designers can develop, in a matter of hours, digital systems containing thousands of gates.
One example of an FPD-based PCB is the "Anyboard" developed at North Carolina State University. The Anyboard consists of a hardware card that incorporates six FPDs (more specifically field programmable gate arrays, or FPGAs), three random access memory (RAM) chips, buffers and local and global buses that connect the FPGAs to the RAMs and buffers. A complete description of the Anyboard system can be found in "Anyboard: An FPGA-based, reconfigurable system," IEEE Design & Test of Computers, pages 21-30, September, 1992, by Van den Bout et al.
While FPD-based PCBs such as the Anyboard provide great flexibility in terms of the variety of circuits that can be developed, to the extent that the architecture of the board is fixed in hardware the application of the board is limited. In case of the Anyboard, for example, the number of FPGAs and RAMs as well as the bus interconnection are fixed in hardware. Improvements have been proposed on the architecture of the Anyboard that require incorporating field programmable interconnect devices (FPIDs) onto the Anyboard. The FPIDs help mitigate the limitations due to fixed bus interconnects. However, a drawback of using FPIDs is the increase in bus delays which limits the speed of the final product.
There is therefore a need for a highly flexible and fast FPD-based universal circuit board with reconfigurable architecture.